SD shows the variation eg caused by biological variation (ie natural) in the data... whereas the SEM gives an indication of the precision of the estimate of the mean (similar to a confidence interval). I always show SEM - since most journals use this etc, SD bars are always way bigger! the bigger your sample size, the smaller the SEM and so the more sure you can be of your estimate of the mean.
I thought I had a handle on this but the more I think about it the more confused I get! personally if reporting stats I'd put in the SD but if displaying on a graph I'd use SE for error bars. Why? I don't really Know that's just what I'd do!
SD gives an idea of the spread of the data. Whilst SE also does the SE also takes into account the number of observations you have, as the greater n you have the smaller the SE. This is not the case with SD.
In some cases it makes sense to use SD. For example if just talking about your sample, such as reporting the age of participants, wheras I think SE relates more to the population - There is a 95% chance the actual mean will fall 1.96*SE from your mean value. Thus it gives an idea of how representative your mean is likely to be of the general popluation.
As for why report SE with t-test, I don't really know. I guess as the t-test measures whether the means are different or whether the error bars overlap, by reporting SE and the mean then an interested reader can check your claims of significance.
PostgraduateForum Is a trading name of FindAUniversity Ltd
FindAUniversity Ltd, 77 Sidney St, Sheffield, S1 4RG, UK. Tel +44 (0) 114 268 4940 Fax: +44 (0) 114 268 5766
An active and supportive community.
Support and advice from your peers.
Your postgraduate questions answered.
Use your experience to help others.
Enter your email address below to get started with your forum account
Enter your username below to login to your account
An email has been sent to your email account along with instructions on how to reset your password. If you do not recieve your email, or have any futher problems accessing your account, then please contact our customer support.
or continue as guest
To ensure all features on our website work properly, your computer, tablet or mobile needs to accept cookies. Our cookies don’t store your personal information, but provide us with anonymous information about use of the website and help us recognise you so we can offer you services more relevant to you. For more information please read our privacy policy
Agree Agree